This invention relates to pattern defect inspection devices for detecting defects in fine repetitive (i.e., periodic) patterns formed, for example, on semiconductor integrated circuits or TFT liquid crystal planar display elements.
FIGS. 1 through 3 schematically show the optical configuration of a typical pattern defect inspection device, which is disclosed, for example, in a technical journal, "Electronics", p. 74, March 1987. FIGS. 1 and 2 show the exposure processes of the Fourier transform filter and the hologram, respectively, while FIG. 3 shows the defect inspection process by which a holographic image (real image) of the defects is formed and examined.
The exposure of the Fourier transform filter is effected as shown in FIG. 1. The light 31 emitted from the laser oscillator 1 and reflected by the reflection mirror 2, beam splitter 3, reflection mirror 4, and reflection mirror 5, is expanded via the beam expander 6. The expanded parallel beam from the beam expander 6 illuminates a specimen (semiconductor wafer) 9 via the reflection mirror 7 and half reflection mirror 8. At this time, a wafer having a normal or proper periodic pattern without any defects is utilized as the specimen 9. (Practically, however, it suffices to use a wafer with only a small number of defects.) The light reflected and diffracted from the repetitive pattern on the specimen (semiconductor wafer) 9 is collected by the lens 10 via the half reflection mirror 8, and forms a spatial frequency pattern (Fourier transform pattern) of the pattern on the specimen 9 on the first photographic plate 11 positioned at the back focal plane of the lens 10. The Fourier transform (spatial frequency) pattern of the pattern on the specimen (semiconductor wafer) 9 without any defects is thus recorded on the first photographic plate 11. The first photographic plate 11 is then developed by a well-known chemical process and is returned to the original position in order to serve as the spatial frequency filter in the subsequent processes described hereinbelow.
Thereafter, the specimen (semiconductor wafer) 9 is replaced by a specimen (semiconductor wafer) which is to be actually inspected and which may have many defects, and the exposure of the second photographic plate 12 is effected as shown in FIG. 2 in order to obtain the hologram of the defects of the pattern on the specimen (semiconductor wafer) 9. The light emitted from the laser oscillator 1 and reflected by the reflection mirror 2 is split into subject beam 31 and reference beam 32 via the beam splitter 3. The subject beam 31 illuminates the specimen (semiconductor wafer) 9 via the same optical path as in FIG. 1. Further, the light reflected and diffracted from the specimen (semiconductor wafer) 9 reaches the first photographic plate 11 via the same optical path as in FIG. 1. Thus, the information corresponding to the normal periodic pattern (i.e., the pattern without defects) on the specimen (semiconductor wafer) 9 is removed from the light passing through the first photographic plate 11, and hence only the information which corresponds to the defects of the pattern on the specimen (semiconductor wafer) 9 reaches the second photographic plate 12. On the other hand, the reference beam 32, reflected via the reflection mirror 13 and the reflection mirror 14, expanded via the beam expander 15, and reflected again via the reflection mirror 16 and the reflection mirror 17, illuminates the second photographic plate 12. Thus, the defect information from the specimen (semiconductor wafer) 9 is recorded on the second photographic plate 12 in the form of a hologram. The second photographic plate 12 is then developed by a well known chemical process and is returned to the original position to serve as the hologram of the defects of the pattern on the specimen (semiconductor wafer) 9.
The inspection of the defects of the specimen (semiconductor wafer) 9 is effected as shown in FIG. 3. The regeneration beam 33 emitted from the laser oscillator 1 is reflected by the reflection mirror 2, transmitted through the beam splitter 3, reflected again by the reflection mirror 13 and reflection mirror 14, and expanded into a parallel expanded beam via the beam expander 15. The expanded beam from the beam expander 15 passing at the side of the reflection mirror 16 moved out of the optical path is reflected by the reflection mirror 18 to illuminate the second photographic plate as the regeneration beam 33 proceeding in the direction opposite to that of the reference beam 32 of FIG. 2 reflected by the reflection mirror 17. Thus, the light passing through the hologram of the pattern defects recorded in the second photographic plate 12 forms, via the first photographic plate, lens 10, and half reflection mirror 8, the holographic image (real defect image) 91 at the position at which the specimen (semiconductor wafer) 9 had been positioned. The optical detector 19 detects the holographic image (real defect image) 91 as the defect information of the pattern on the specimen (semiconductor wafer) 9.
The above conventional pattern defect inspection device, however, has the following disadvantage. The device is in need of the first photographic plate serving as the spatial frequency filter and the second photographic plate serving as the hologram of the defects of the pattern on the specimen. Thus, the pattern defect inspection device is complicated in organization and hence is large is size.